In recent years, the third generation mobile communication (3G) including W-CDMA systems has been in widespread use on a worldwide basis. Currently, the fourth generation mobile communication (4G) has further been considered to implement communication rates of 100 Mb/s to 1 Gb/s on downlink. However, it is not easy to completely shift from 3G to 4G. Therefore, attention is directed toward E-UTRA (Evolved-UTRA) for increasing the rate in communication using a frequency band of 3G while introducing new techniques of 4G. Active proposals have been made also in 3GPP (3rd Generation Partnership Project).
In the mobile communication system, a mobile station needs to identify a cell and a section to which the mobile station intends to connect for initial synchronization establishment or handover. In other words, it is necessary to detect a base station targeted for communication and an antenna of the base station. In the third generation mobile communication, the so-called 3-step cell search method is adopted to perform a fast cell search. In addition, the concept of “cell search” includes “sector search”.
The 3-step cell search in the third generation mobile communication generally uses a Synchronization Channel (SCH) and a Common Pilot Channel (CPICH). First, the reception timing of the SCH is detected (first step), and next, identification of the frame timing and a scramble code group is performed by correlation detection with the SCH code (second step). Then, a scramble code is identified by correlation detection using the CPICH (third step).
In the E-UTRA that is the next generation mobile communication standard, OFDM (Orthogonal Frequency Division Multiplexing) is used as a modulation scheme, and regarding the cell search, techniques following the philosophy of the above-mentioned 3-step cell search are proposed (for example, see Patent Document 1, Patent Document 2, Non-patent Document 1 and Non-patent Document 2).
Patent Document 1 discloses techniques for frequency-multiplexing a second synchronization code (S-SCH signal) for scramble code group identification on a plurality of subcarriers in the 3-step cell search in the multicarrier communication system adopting OFDM.
Patent Document 2 discloses techniques for multiplexing a cell identification code on a Common Pilot Channel (CPICH) in the 3-step cell search in the multicarrier communication system adopting OFDM.
Moreover, Non-patent Document 1 proposes standardization of a one-cell reuse communication system adopting OFDM. Further, a draft of standardization has been proposed in consideration of a base station provided for each sector concurrently performing communications with a plurality of mobile stations in the cell. In this technique, the Common Pilot Channel (CPICH) is doubly multiplied by a spreading code specific to a cell and a spreading code specific to a sector. Accordingly, a mobile station performs despreading and correlation detection using each spreading code replica, and is thereby capable of identifying the cell (and the sector).
Further, Non-patent Document 2 discloses techniques for identifying a cell (and a sector) by a 3-step cell search similar to techniques of the third generation in the multicarrier communication system adopting OFDM. In the techniques, as in the techniques disclosed in Non-patent Document 1, a cell is divided into three sectors, and the same Synchronization Channel code (SCH code) is used among the sectors. With respect to transmission of the SCH code, time synchronization is acquired among the sectors, and transmission of the SCH for each sector is performed at the same time. Then, identification of a cell and a sector i.e. selection of a cell and a sector providing the maximum reception power is made by correlation detection with replicas of spreading codes using a pilot channel in the third step.
Thus, also in the E-UTRA that is the next generation communication standard, proposals are made to adopt the techniques following the 3-step cell search of 3G using the SCH and CPICH. Particularly, with respect to sector identification, as disclosed in Non-patent Documents 1 and 2, the Common Pilot Channel is multiplied by a spreading code specific to a sector, and a sector providing the maximum reception power is detected by despreading and correlation detection processing in the third step.
Patent Document 1: Japanese Laid-Open Patent Publication No. 2003-179522
Patent Document 2: Japanese Laid-Open Patent Publication No. 2005-198232
Non-patent Document 1: 3GPP “TR 25.814, “Physical Layer Aspects for Evolved UTRA (Release 7) v.0.3.1” Oct. 18, 2005
Non-patent Document 2: 3GPP “R1-060042, “SCH Structure and Cell Search Method in E-UTRA Downlink” Jan. 25, 2006